1. Field of the Invention
The present invention relates to rotating media storage devices (RMSDs). More particularly, the present invention relates to an RMSD that has at least one calibration track with unique calibration servo synch marks (SSMCs).
2. Description of the Prior Art and Related Information
Computer systems rely on rotating media storage devices (RMSDs), which often employ a moveable head actuator to frequently access large amounts of data stored on the media. One example of an RMSD is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the transducer head over a particular track on the disk to read or write information from and to that track, respectively.
With reference to FIG. 1, FIG. 1 shows an example of a prior art disk 10 having a plurality of concentric tracks 12. Each surface of each disk 10 conventionally contains a plurality of concentric data tracks 12 angularly divided into a plurality of data sectors 15. In addition, special servo information is provided on each disk to determine the position of the moveable transducer head. These tracks 12 are typically referred to as normal tracks.
The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo wedges 14a, 14b, etc. that are angularly spaced from one another and are interspersed between data sectors 15 around each track of each disk.
Each “Full” servo wedge 14 typically includes a phase lock loop (PLL) field 20, a servo synch mark (SSM) field 22, a track identification (TKID) field 24, a wedge ID field 26 having a binary encoded wedge ID number to identify the wedge, and a group of servo bursts (e.g. ABCD 28—an alternating pattern of magnetic transitions) which the servo control system samples to align the moveable transducer head with or relative to a particular track. In some instances, the servo wedge 14 may only include servo bursts 28 and is referred to as a “Mini-Wedge.” This allows for a smaller servo wedge and allows for more space on the track to be devoted to user data.
Typically, the servo control system moves the transducer head toward a desired track during a coarse “seek” mode using the TKID field as a control input. However, in processing information, it is necessary to ensure consistency in the detection of bits composing a block of bits. One common approach directed to ensuring such consistency employs multiple stored fields including a phase lock loop (PLL) field 20 to facilitate bit synchronization and a synch field to facilitate block synchronization. The synch mark field facilitates block synchronization by holding a special marker that is detected to “frame” data, i.e., to identify a boundary of a block. In contemporary hard disk drives employing embedded servos, it is well known to provide framing of servo data via a servo synch mark (SSM) field 22.
Generally, in hard disk drives, a servo synchronization signal based on the head reading a servo synchronization mark (SSM) results in a read/write channel of the disk drive establishing a precise timing reference point for read/write operations.
Once the transducer head is generally over the desired track, the servo control system uses the servo bursts (e.g. ABCD) 28 to keep the transducer head over the track in a fine “track follow” mode. During track following mode, the moveable transducer head repeatedly reads the wedge ID field 26 of each successive servo wedge 14 to obtain the binary encoded wedge ID number that identifies each wedge of the track. In this way, the servo control system continuously knows where the moveable head is relative to the disk.
In some systems, “Mini-Wedges” only having servo bursts 28 are utilized in addition to the “Full Wedges.” For example, once the servo control system has acquired the requisite information needed for track following from the Full Wedges, track following can be maintained using the Mini-Wedges. Use of Mini-Wedges allows for a smaller servo wedge and for more space on the track to be devoted to user data, but requires more computationally intensive servo control.
In many of today's disk drives, diagnostic and calibration functions are performed with the aid of specialized calibration tracks. As shown in FIG. 1, typically calibration tracks are located at the outer diameter and the inner diameter of a disk, such as outer diameter calibration track 13A and inner diameter calibration track 13B. Particularly, the calibration tracks are utilized by the servo control system for diagnosis and calibration purposes.
Turning to FIG. 2, FIG. 2 illustrates an example of calibration tracks at the outer and/or inner diameter of a typical disk drive. Generally, a calibration track includes a plurality of normal servo wedges, which may be Full Wedges or Mini-Wedges, distributed around the calibration track. Further, a plurality of calibration wedges are distributed between the normal wedges. FIG. 2 only shows two calibration servo wedges 29, however, it should be appreciated that dependent upon design considerations, any number of calibration servo wedges may be utilized. Typically, during a calibration mode, the servo control system seeks and locks to the normal wedges 14, and then switches to a new sampling period to read both normal and calibration wedges in order to perform any needed diagnostic and calibration functions.
There are many problems associated with the previously described configuration of calibration tracks used in current disk drives. For example, when full wedges are utilized as the calibration servo wedges, the servo control system of the disk drive may accidentally lock onto one of the full calibration servo wedges 29 of one of the calibration tracks 13, instead of one of the full normal wedges 14 of a non-calibration track, resulting in a timing error and possibly causing the disk drive to fail. This is because there is no difference between the servo synch mark (SSM) utilized in the full calibration servo wedges of calibration tracks and the full normal servo wedges of non-calibration tracks. Further, when Mini-Wedges are utilized for the calibration servo wedges, the servo control that needs to be utilized to track along the Mini-Wedges is very computationally intensive.